A study on defect tolerance of tiles implementing universal gate functions

Quantum-dot cellular automata (QCA) are considered as the future alternative to state-of-the- art CMOS designs. The tile structures for the QCA circuit elements are proposed to enable effective modular design. This work introduces 3times3 tile structures for realizing the NNI (nand-nor-inverter) as well as the AOI (and-or-inverter) logic. The defect characterizations for such tiles are carried out to comment on the stability of designs. It analyzes the effect of cell deposition as well as the cell misplacement defects. The study on defective tiles point to the fact that the NNI tile is more defect tolerant than AOI under deposition defects. However, an AOI tile is comparatively less sensitive to misplacement of input/output. It is further noted that the AOI tiles display better detectability of multiple cell deposition defects than that of an NNI tile.